Volume of a sphere is 4/3 π r^3 .

Solving for r where the volume is 4000 cm^3 makes for a 9.8 cm radius, or a 19.6 cm (7.7 inch) diameter. Comparable to a child size 3 soccer ball.

Obviously taking a soft sphere and letting it flatten on a surface against its own weight makes for a non-spherical shape, but this picture looks way bigger than a kid's soccer ball.